Relapse to cocaine use is a major barrier to successful treatment outcome. This research proposes to inititate a program of research for a new investigator interested in preventing relapse in homeless persons with cocaine use (primarily crack cocaine) disorders. It proposes to use ecological momentary assessment techniques (repeated surveying of subjects by cellular phone) to acquire real-time and near real time information about daily events in treatment participants' lives related to relapse and near-relapse events. The first aim is to develop a survey for use with a cellular phone assessment of lapse and relapse (the CALLER intrument) by adapting existing smoking relapse surveys used for real time assessment by Shiffman and colleagues. The second aim is to pilot test a computerized momentary assessment procedure by administering it via cellular telephone, to day treatment program particpants with a DSM IV Axis I cocaine use disorder. Participant feedback will be utilized to create a second generation survey for reliability and validity testing. The third aim will assess the reliability of the CALLER instrument using test-retest methodology. The fourth aim will be to assess the validity of the CALLER instrument by comparing relapse and relapse risk data to urine drug toxicology results, a standard retrospective "time-line follow-back" instrument, and an established cocaine relapse instrument, the Cocaine Relapse Interview (McCay et al, 1996). This study will demonstrate whether ecological momentary assessment is feasible with crack cocaine users, and add to the available existing methods to study relapse to cocaine use. This research will test for crack cocaine users, the assumptions of Marlatt and Gordon's theory that failure to cope in high risk situations results in relapse and that attributions regarding lapses lead to relapse (1985). Knowledge derived from development and testing of the innovative assessment methodology could contribute to long-term improved treatment outcome.